Which of these numbers is composite? ${11,\ 37,\ 61,\ 77,\ 79}$
Explanation: A composite number is a number that has more than two factors (including 1 and itself). 11, 37, 61, and 79 each have only two factors. The factors of 77 are 1, 7, 11, and 77. Thus, 77 is the composite number.